Water management is a success story, how water quality changed based on historical development and mid-term hydroclimate.

Urban water quality has traditionally been perceived as primarily influenced by point sources such as wastewater treatment plants and (combined) stormwater overflows. However, limited attention has been given to understanding how the urban stream syndrome evolves post the operation of water management facilities, the broader impacts on water quality beyond these measures, and the influence of hydroclimate on urban water quality. In this study, we present spatially distributed data spanning 66 years of water quality and fertilizer application, 30 years of water quantity, and 20 years of groundwater quality in the urban Panke catchment, Berlin, Germany, aiming to address these questions. Hydroclimatic indicators, specifically the Standard Precipitation Index (SPI), were employed, and the data was analyzed for trend delineation, breakpoint analysis, and concentration-discharge relationships. Predictably, major water quality changes were attributed to shifts in water management practices, such as the transformation of the former sewage irrigation farm, subsequent replacement with a wastewater treatment plant, and alterations in wastewater redirection. Interestingly, unaffected upstream sites were parallel improving in water quality. While concentration-discharge remained unaffected by hydroclimate, we observed trends towards lower NO3-N and higher NH4-N, oPO3-P, and CL concentrations during droughts. Despite these variations, the upstream sites demonstrated significant overall improvement, reaching the highest water quality classification, demonstrating how effective water management can enhance resilience. The hydrochemical dynamics in upstream sites suggested altering connectivity during drought, which remains unclear and requires further investigation. Beyond our research findings, we highlight the importance of establishing a structured, long-term monitoring program and promoting knowledge transfer across various institutions. This collaborative approach is deemed crucial for comprehending and contextualizing the gathered data.